System and method for laser range-finding

ABSTRACT

A system and method is described for determining a distance to a desired target via correlating a pulse modulated signal with its corresponding reflected signal, while compensating for noise error in the reflected signal to allow for a more precise distance determination. Further details and features are described herein.

BACKGROUND

Laser range finders are commonly implemented based on a measurement ofthe round trip delay of a signal echoed by a target. For example, theround trip delay is multiplied by the speed of light (c) to determinethe total back and forth distance to the target. Currently, there arevarious methods for determining the round trip delay. These methods maydirectly or indirectly determine the round trip delay.

One direct method includes measuring the time of flight (TOF) of atransmitted pulse of light. However, measuring the time of flight of apulse requires fast electronics that limits this method to long rangemeasurements. Some indirect methods include measuring the phase shift ofa periodic signal, beat frequency of a chirped waveform, or a crosscorrelation of a shifted image of the transmitted signal with its echo.The indirect methods which are based on periodic signal analysis aremore adapted to short or medium range distances. For example, it ispossible to extract longer delays from a beat frequency determination,because the beat frequency is easier to measure using commonelectronics.

In the cross correlation method, the amount of phase shift of atransmitted signal that is needed to obtain the maximum correlationvalue represents the traveling delay of the light pulse. In other words,the round trip delay is determined by the amount the transmitted signalshould to be delayed to obtain maximum correlation with its echoedsignal. Such method employs a point in time comparison of a point(s) onthe transmitted signal with a same point(s) on the echoed signal todetermine the phase shift. The accuracy of such comparison is heavilydependant on the amount of noise contained in the echoed signal. Noiseerror in echoed signals are common, especially in long rangetransmission.

Thus, the need exists for a system and method that provide compensationfor noise error in echoed signals such that more accurate phase shiftscan be determined to allow accurate measurements of long distances totargets, as well as a system and method that provides additionalbenefits such as a simplified and cost effective system structure.Overall, the examples herein of some prior or related systems and theirassociated limitations are intended to be illustrative and notexclusive. Other limitations of existing or prior systems will becomeapparent to those of skill in the art upon reading the followingDetailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system level schematic illustration of a system operable toimplement aspects of the invention.

FIG. 2 is a schematic illustration of the system of FIG. 1, including acorrelator used to implement aspects of the invention.

FIG. 3 is a high-level flow diagram of a method for implementing aspectsof the invention.

FIG. 4 is a graphical representation of the method of FIG. 3.

FIG. 5 is a low-level flow diagram of a portion of the method of FIG. 3.

FIG. 6 is a schematic illustration of a system incorporating apolarizing splitter to implement aspects of the invention.

The headings provided herein are for convenience only and do notnecessarily affect the scope or meaning of the claimed invention.

In the drawings, the same reference numbers and any acronyms identifyelements or acts with the same or similar structure or functionality forease of understanding and convenience. To easily identify the discussionof any particular element or act, the most significant digit or digitsin a reference number refer to the Figure number in which that elementis first introduced (e.g., element 202 is first introduced and discussedwith respect to FIG. 2).

DETAILED DESCRIPTION

Various examples of the invention will now be described. The followingdescription provides specific details for a thorough understanding andenabling description of these examples. One skilled in the relevant artwill understand, however, that the invention may be practiced withoutmany of these details. Likewise, one skilled in the relevant art willalso understand that the invention incorporates many other obviousfeatures not described in detail herein. Additionally, some well-knownstructures or functions may not be shown or described in detail below,so as to avoid unnecessarily obscuring the relevant description.

The terminology used below is to be interpreted in its broadestreasonable manner, even though it is being used in conjunction with adetailed description of certain specific examples of the invention.Indeed, certain terms may even be emphasized below; any terminologyintended to be interpreted in any restricted manner will, however, beovertly and specifically defined as such in this Detailed Descriptionsection. A “reflected” signal refers to a signal that is an echo orreflection of a transmitted signal that is incident on an object. Thereflected signal may be equivalent to the transmitted signal attenuatedby noise corruption and/or a reduced energy level. Additionally and/oralternatively, the reflected signal may comprise an average of first andsecond echoes or reflections in response to incidence of respectivefirst and second polarizations of the transmitted signal onto theobject. A “reference” signal refers to a calibrated version of thetransmitted signal. The reference signal may include the transmittedsignal attenuated with an amplitude that substantially matches that ofthe “reflected” signal. For example, the reference signal may beequivalent to the transmitted signal having an amplitude of 1.

Various formulas throughout the specification and claims make referenceto f_(sent)(t) and f_(reflected)(t), which correspond to a function overtime of the transmitted and reflected signals, respectively.

System Description

FIG. 1 and the following discussion provide a brief, general descriptionof a suitable environment in which the invention can be implemented.Although not required, aspects of the invention are described below inthe general context of computer-executable instructions, such asroutines executed by a general-purpose data processing device, e.g., anetworked server computer, mobile device, or personal computer.

Aspects of the invention may be stored or distributed on tangiblecomputer-readable media, including magnetically or optically readablecomputer discs, hard-wired or preprogrammed chips (e.g., EEPROMsemiconductor chips), nanotechnology memory, biological memory, or otherdata storage media. Alternatively or additionally, computer implementedinstructions, data structures, screen displays, and other data underaspects of the invention may be distributed over the Internet or overother networks (including wireless networks), on a propagated signal ona propagation medium (e.g., an electromagnetic wave(s), a sound wave,etc.) over a period of time, or they may be provided on any analog ordigital network (packet switched, circuit switched, or other scheme).

FIG. 1 shows a schematic illustration of a system 100 a for determininga distance to a target 108 via correlating a pulse modulated signal withits corresponding reflected signal. The system 100 a comprises atransmitter 102, a detector 104, and a correlator 106.

The transmitter 102 may, for example, be a laser transmitter such as alaser diode, a light transmitter, or a signal generator. The lasertransmitter is a device that emits light (i.e., electromagneticradiation) through a process called stimulated emission. The light iseither emitted as a narrow or low-divergence beam, or can be convertedinto one via optical components such as lenses. Some laser transmittersemit light with a broad spectrum, while others emit light at multipledistinct wavelengths simultaneously. The coherence of typical laseremission is distinctive. Most other light sources emit incoherent light,which has a phase that varies randomly with time and position.

The transmitter 102 is configured to transmit a signal T, for example alaser beam of light, which is modulated by a modulation component 103(illustrated in FIG. 2), such as a pulse modulation component. Themodulation component 103 modulates the transmitted signal T at a definedfrequency f_(m). The transmitted signal T is modulated by one or morepulses such as, for example, via pulse code modulation (PCM). These oneor more pulses may, for example, take the form of triangular pulses,rectangular pulses, square pulses, or trapezoidal pulses. Pulsemodulation (e.g. pulse code modulation) may be advantageouslyimplemented to minimize the interference or distortion of the reflectedsignal over long distances.

The defined frequency of modulation f_(m) may be determined based on anexpected distance to the target 108. In other words, it is well known inthe art that the distance to the target 108 of interest is provided bythe following equation:

${L = {\frac{1}{2}c\frac{\Delta\phi}{2{\pi \cdot f_{m}}}}},$

where f_(m) is the modulation frequency; Δφ is a phase shift of an echoof the transmitted signal; c is the speed of light (i.e., 3×10⁸ m/s);and L is the distance to the target 108.

The distance L that is to be measured is limited by the pulse modulationfrequency f_(m) of the transmitted signal T. To avoid ambiguity whenΔφ=2π, a condition Δφ<2π may advantageously be satisfied. For example,for a modulation frequency f_(m) of 30 MHz, the maximum distance L thatcan be measured is 5 meters. In some embodiments, the modulationfrequency f_(m) may be periodically changed according to a definedsequence. The target 108 may be any object having physical properties orcharacteristics that cause a signal (e.g., light or laser beam)transmitted thereon to be at least a partially reflected.

The transmitted signal T (illustrated in FIG. 4) is incident on thetarget 108 and then reflected back toward the detector 104. Thereflected signal R (as illustrated in FIG. 4) may include noise errorand thus may be distorted. Noise error may be due to the physicalcharacteristics of the target 108 which affect signal reflection and/orrandom noise incurred during transmission/reception. Additionally, thereflected signal R may have a lower power level than the transmittedsignal T due to, for example, absorption of energy by the target 108.

The detector 104 may, for example, be a light sensor or photo-detector,including a semiconductor device such as a photocell, photodiode,phototransistor, CCD (Charged Couple Device), image sensor (e.g., CMOSimager), or any other sensing device. The photo-detector may be operableto convert the reflected signal R into either current or voltage,depending upon the mode of operation. The detector 104 iscommunicatively coupled to the correlator 106 and is operable to receivethe reflected signal R and communicate the reflected signal R to thecorrelator 106.

As illustrated in FIG. 1, the correlator 106 is communicatively and/orelectrically coupled to both the transmitter 102 and the detector 104.For example, the correlator 106 may be coupled to the transmitter 102and the detector 104 via wired and/or wireless connection. Thecorrelator 106 is operable to employ a correlation (e.g.,cross-correlation or convolution) of the transmitted signal T with thereflected signal R to determine a phase shift 129 (illustrated in FIG.4) such as, for example, a time shift (or time delay). As mentionedabove, the reflected signal R may have substantially less power than thetransmitted signal T. In some embodiments, since the correlator 106calculates the correlation (to be discussed in detail herein) using thetransmitted signal T as a reference, the correlator 106 may perform acalibration of the transmitted signal T to advantageously match theamplitude of the reflected signal R. For example, the correlator 106 maybe configured to normalize the amplitude of its received transmittedsignal T to 1, thereby simplifying the calculation as will be discussedherein. The calibrated (or normalized) transmitted signal T will bereferred to herein as the “reference” signal.

The correlator 106 is configured to determine: (1) a sum of mutualsamples in time of the transmitted and reflected signals T, R within arespective one of the modulation pulses; and (2) a sum of samples intime within the respective one of the modulated pulses of the reflectedsignal R. Based on such determination, the correlator 106 can readilycalculate the phase shift 129 (e.g., time shift) between the transmittedand reflected signals T, R, as will be discussed in detail below. Thecorrelator 106 ascertains the distance L to the target 108 based on thecalculated phase shift 129 (e.g., time shift) and the modulationfrequency f_(m) using the equation:

${L = {\frac{1}{2}c\frac{\Delta\phi}{2{\pi \cdot f_{m}}}}},$

where Δφ corresponds to the phase shift 129.

FIG. 2 shows a schematic illustration of the correlator 106, accordingto one illustrated embodiment. The correlator 106 may include a signalgenerator 105, a calibration component 110, a cross-correlator 112, aband pass filter 114, an analog-to-digital converter (ADC) 116, samplingcomponent 118, a filter 120, and a processor 122.

The calibration component 110 may be coupled to receive the transmittedsignal T from the modulation component 103 and configured to normalizethe transmitted signal T, thereby creating the reference signal. Thereference signal may be such that its amplitude is similar to that ofthe reflected signal R. For example, the calibration component 110 maynormalize the transmitted signal T and create the reference signal withan amplitude of 1.

The cross-correlator 112 may be coupled to receive, as inputs, thereference signal and the reflected signal R from the calibrationcomponent 110 and the detector 104, respectively. The cross-correlator112 may, for example, take the form of a product (or multiplying) mixersuch as a Gilbert cell mixer, diode mixer, diode ring mixers (i.e., ringmodulation), switching mixer, or multiplier followed by a short termintegrator to sum the multiplier product over the specified shortinterval. A product mixer multiplies signals and produces an outputincluding both original signals, and new signals that have the sum anddifference of the frequency of the original signals. Ideal productmixers act as signal multipliers, producing an output signal equal tothe product of the two input signals. Product mixers are often used inconjunction with an oscillator to modulate signal frequencies. Productmixers can either up-convert or down-convert an input signal frequency,but it is more common to down-convert to a lower frequency to allow foreasier filter design. In many typical circuits, the single output signalactually contains multiple waveforms, namely those at the sum anddifference of the two input frequencies and harmonic waveforms. Theideal signal may be obtained by removing the other signal componentswith a filter (e.g., band pass filter).

The cross-correlator 112 may multiply the reference and the reflectedsignals and produce an output signal comprising the product of thesesignals. The product of the reference and reflected signals will bereferred to herein as the “product signal.” The band pass filter 114 isconfigured to remove other signal components (e.g. waveforms) that maybe included in the product signal generated by the cross-correlator 112.The band pass filter 114 may, for example, be a device or circuit thatpasses frequencies within a certain range and rejects (or attenuates)frequencies outside that range. Further details of cross-correlators,mixers and filters may be found in commonly assigned U.S. patentapplication Ser. No. 12/254,733, filed Oct. 20, 2008 and entitled “LASERBARCODE SCANNER EMPLOYING HETERODYNING TECHNIQUES,” which is herebyincorporated by this reference in its entirety.

The analog-to-digital converter (ADC) 116 is coupled to receive theproduct signal from the band pass filter 114 and configured to convertthe product signal to digital form by sampling. The sampling component118 may define the sampling rate of the ADC 116 based on the modulationfrequency f_(m) of the modulation pulses. For example, the higher themodulation frequency, the higher the sampling rate. The samplingcomponent 118 may be configured such that the defined sampling rate isabove the nyquist rate.

Upon conversion of the product signal to the digital (or discrete)format, the digital product signal may, for example, be forwarded to theprocessor 122 via the additional filter 120 to remove an aliasing signaloriginating from the cross-correlator 112 and to determine the sum ofmutual samples in time of the reflected and reference signals.Additionally, the processor 122 may receive the reflected signal R uponbeing digitized via the ADC 116 and passed through the filter 120. Theprocessor 122 determines the sum of samples in time within the modulatedpulse of the digitized reflected signal R. As will be described in themethod of FIGS. 3-5, based on these determinations, the processor 122measures the phase shift 129, which is ultimately used to calculate thedistance L to the target 108, as defined by the equation:

$L = {\frac{1}{2}c{\frac{\Delta\phi}{2{\pi \cdot f_{m}}}.}}$

The processor 122 may, for example, take the form of a microprocessor,microcontroller, application-specific integrated circuit (ASIC), ordigital signal processor (DSP) configured to execute various DSPalgorithms. For example, the processor 122 may be operable to executeFFT (Fast Fourier Transform) or any other digital transform algorithmsto manipulate digital data received, for example, from the ADC 116. Asis known in the art, the processor 122 may comprise a battery powersource, a memory, a trigger, and optics. The processor 122 may beembedded within the correlator 106 (as illustrated in FIG. 2), while inother embodiments the correlator 106 may have access to the processor122 positioned outside the correlator 106. Additionally and/oralternatively, the correlator 106 may comprise or have access to one ormore processors operating in conjunction or separately.

Method Description

FIG. 3 shows a high-level flow diagram of a method 300 for determiningthe distance L to the target 108 based on the phase shift 129 (e.g. timeshift) between the transmitted signal T and the reflected signal R,according to one embodiment, while FIG. 4 shows a graphicalrepresentation of the method of FIG. 3.

Specifically, FIG. 4 graphically illustrates how the method 300determines a fraction:

$\left( {{i.e.},\frac{\int{{f_{sent}(t)}*{f_{reflected}(t)}{t}}}{\int{{f_{reflected}(t)}{t}}},} \right.$

where f_(sent)(t) and f_(reflected)(t) correspond to a function overtime of the transmitted and reflected signals T, R, respectively) of atotal area of the transmitted signal T pulse that corresponds to thephase shift 129 by measuring a mutual area between the transmittedsignal T pulse and the reflected signal R pulse. The method 300 may beimplemented by the correlator 106. It will be appreciated by thoseskilled in the art that aspects of the correlator 106 are not limited tothe embodiment illustrated in FIG. 2. Various other embodiments may beimplemented to perform the method 300 described herein.

The method 300 starts, for example, in response to the correlator 106receiving the transmitted signal T and the reflected signal R from thetransmitter 102 and the detector 104, respectively.

Optionally at 302, the calibration component 110 converts thetransmitted signal T into the reference signal upon normalizing thereceived transmitted signal T, which was transmitted to the target 108.The normalization may be such that the amplitude of the reference signalis made similar to that of the reflected signal R. For example, thetransmitted signal T may be normalized to obtain a reference signal withan amplitude of 1. Such normalization may simplify the calculation ofthe phase shift 129, as described in the method of FIG. 5.

At 304, the correlator 106 determines a first sum of points in timewithin an overlap region of the transmitted and reflected signals T, R.The overlap region of these signals is the region of overlap within bothof the modulated pulses. In other words, the correlator 106 calculates asum of mutual samples in time of the transmitted and reflected signalsT, R. This first sum of points may be determined by calculating an area125 of the overlap region.

At 306, the correlator 106 determines a second sum of points in timewithin one of the modulated pulses of the reflected signal R. The secondsum of points will be the total sum of points within the modulated pulseof the reflected signal R. The second sum of points may be determined bycalculating an area 127 of the modulated pulse of the reflected signalR.

At 308, the correlator 106 determines a portion of the transmittedsignal T that is overlapped by the reflected signal R (or mutual to thereflected signal R). The ratio of the first sum of points in the overlapregion of the two signals to the second sum of points within themodulated pulse of the reflected signal R is calculated to determine theportion of the transmitted signal T that is mutual to the reflectedsignal R. In other words, the ratio of the first sum of points to thesecond sum of points determines the portion of the transmitted signal Tthat is overlapped. The determination of the portion of the transmittedsignal T that is overlapped by the reflected signal R may, for example,be determined by calculating a ratio of the area 125 of the overlapregion to the area 127 of the modulated pulse of the reflected signal R.

At 310, the correlator 106 determines the phase shift 129 between thetransmitted and reflected signals T, R. Under ideal conditions, thereflected signal R is not corrupt with noise nor do the characteristicsof the target 108 influence the reflection of the transmitted signal T.Thus, ideal conditions dictate that the reflected signal R is a perfectreflection of the transmitted signal T. In other words, identicaloverlap would ideally be established between the pulses of thetransmitted and reflected signals T, R. Consequently, under idealconditions, a ratio of a sum of samples in time of a pulse of thetransmitted signal T to a sum of samples in time of a pulse of thereflected signal R would be equal to 1.

The correlator 106 subtracts the portion of the transmitted signal Tthat is mutual to the reflected signal R (calculated in step 308) from 1(i.e., ideal circumstance of perfect overlap and no phase shift) toobtain the phase shift 129. If the time shift is desired, the phaseshift 129 may be multiplied by half a time duration (t₂-t₁) of therespective one of the modulated pulses.

At 312, the correlator 106 calculates the distance L to the target 108based on the phase shift 129 determined at step 310 and the modulationfrequency f_(m). The correlator 106 applies the equation:

$L = {\frac{1}{2}c\frac{\Delta\phi}{2{\pi \cdot f_{m}}}}$

to determine the distance L to the target 108. Alternatively, if thetime shift was determined in step 310, the correlator 106 applies theequation: L=c×Δt, where Δt is the time shift, to determine the distanceL to the target 108.

FIG. 5 shows a low-level flow diagram of a portion of the method 300 ofFIG. 3, specifically steps 304-308, according to one embodiment.

At 304, the correlator 106 determines the first sum of points in timewithin the overlap region of the transmitted and reflected signals T, Rby calculating a convolution of the transmitted and reflected signals T,R:

∫f_(sent)(t)*f_(reflected)(t)dt

If the transmitted signal T was normalized to 1, such that

${f_{sent}(t)} = \left\{ \begin{matrix}{1,} & {t_{1} < t < t_{2}} \\{0,} & {{else},}\end{matrix} \right.$

the convolution of the two signals would simply be equivalent to theintegral over time of the reflected signal R within the overlap region,

∫_(t₁)^(t₂)f_(reflected)(t) t.

Thus, normalizing the transmitted signal T may advantageously simplifythe calculation and reduce overall processing time.

At 306, the correlator 106 determines the second sum of points in timewithin one of the modulated pulses of the reflected signal R bycalculating an integral over time of the modulated pulse of thereflected signal R. For example, the second sum of points may berepresented by: ∫f_(reflected)(t)dt.

At 308, the correlator 106 determines a portion of the transmittedsignal T that is overlapped by (or mutual to) the reflected signal Rupon calculating a ratio of the convolution of the transmitted andreflected signals T, R to the integral over time of the modulated pulseof the reflected signal R:

$\frac{\int{{f_{sent}(t)}*{f_{reflected}(t)}{t}}}{\int{{f_{reflected}(t)}{t}}}$

If, for example, the transmitted signal T is normalized to 1, theportion of the transmitted signal T that is overlapped by (or mutual to)the reflected signal R is calculated by a simplified equation of:

$\frac{\int_{t_{1}}^{t_{2}}{{f_{reflected}(t)}\ {t}}}{\int_{t_{1}}^{t_{3} - ɛ}{{f_{reflected}(t)}\ {t}}}.$

At 310, the correlator 106 determines the phase shift 129 between thetransmitted and reflected signals T, R. As discussed above, under idealconditions, there is identical overlap between the modulated pulses ofthe transmitted and reflected signals T, R, and no phase shift arises.Consequently, under ideal conditions, a ratio of an integral over timewithin an overlap region of the transmitted and reflected signals T, Rto an integral over time of a modulated pulse of the reflected signal Rwould yield a value of 1.

If the transmitted and, therefore, received signals T, R arerectangular, the above ratio is a linear function of the distance L tothe target 108. However, in some embodiments, for example, thetransmitted signal T could be a sine or Gaussian Monocycle; therefore,it may be advantageous to calibrate the correlator 106 and create alook-up-table (LUT) for specific ratio values corresponding toparticular phase shifts 129. For example, the correlator 106 may accessthe LUT to determine the phase shift 129 corresponding to the specificratio value (i.e., the portion of the transmitted signal T that isoverlapped by (or mutual to) the reflected signal R) calculated at 308.

The correlator 106 subtracts the portion of the transmitted signal Tthat is mutual to the reflected signal R (calculated in step 308) from 1(i.e., ideal circumstance of perfect overlap and no phase shift), toobtain the phase shift 129. If the time shift is desired, the phaseshift 129 may be multiplied by half the time duration (t₂−t₁) of therespective one of the modulated pulses.

Alternative System Description

FIG. 6 shows a system 100 b for determining the distance to the target108 based on phase shifts (e.g. time shift) associated with a first anda second polarization of the transmitted signal T.

A polarizing splitter 160, such as a beam splitter (e.g., laser beamsplitter) may be positioned in the path of the transmitted signal T(e.g. laser beam) prior to incidence on the target 108. The polarizingsplitter 600 may split the transmitted signal T into first and secondsignals p, s, respectively, having different polarizations. A signal(e.g., light beam) polarized in a plane of incidence is referred to asbeing p-polarized, while a signal (e.g., light beam) polarizedperpendicular to the plane of incidence is referred to as s-polarized.In our case, the first and second polarized signals p, s, arep-polarized and s-polarized, respectively. The polarization of the firstand second signals p, s may be symmetrical or non-symmetrical. Forexample, polarization of the first and second signals p, s may be atleast one of orthogonal, linear, circular, and elliptical polarization(e.g., ⅓ and ⅔ polarization, respectively).

Additionally, a mirror 162 or similar reflective component or surfacehaving minimal absorption characteristics, may be implemented in thesystem 100 b to advantageously reflect the second signal s(s-polarization) in the direction of the plane of incidence. The mirror162 allows for incidence of the second signal s onto the target 108 inaddition to the first signal p (p-polarization). In response toincidence of the first and second signals p, s on the target 108, firstand second reflected signals p′, s′ are generated. It is well known inthe art that two signals having different polarization will be reflecteddifferently. For example, the first reflected signal p′ may have lessnoise error than the second reflected signal s′.

The detector 104 is configured to detect the first and second reflectedsignals p′, s′ and forward to the correlator 106 for processing. Thecorrelator 106 averages the first and second reflected signal p′, s′.The correlator 106 may, for example, average the weighted coefficientsof the first and second reflected signal p′, s′ to determine thereflected signal R of FIGS. 1-5, which is used to calculate the phaseshift 129 (or time shift) and ultimately the distance L to the target108. Such averaging of the first and second reflected signals p′, s′provides additional compensation for potential noise error produced bythe first and second reflected signals p′, s′ and thus advantageouslyprovides a more accurate determination of the distance L to the target108.

It will be understood by those skilled in the art that once the firstand second reflected signal p′, s′ are averaged to determine thereflected signal R, the system 100 b may implement the methods 300, 500of FIGS. 3 and 5, and various acts described with regard to the system100 a components.

CONCLUSION

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” As used herein, the terms “connected,”“coupled,” or any variant thereof means any connection or coupling,either direct or indirect, between two or more elements; the coupling orconnection between the elements can be physical, logical, or acombination thereof. Additionally, the words “herein,” “above,” “below,”and words of similar import, when used in this application, refer tothis application as a whole and not to any particular portions of thisapplication. Where the context permits, words in the above DetailedDescription using the singular or plural number may also include theplural or singular number respectively. The word “or,” in reference to alist of two or more items, covers all of the following interpretationsof the word: any of the items in the list, all of the items in the list,and any combination of the items in the list.

The above Detailed Description of examples of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific examples for the invention are describedabove for illustrative purposes, various equivalent modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize. For example, while aspects of the inventionare described above with respect to capturing and routing digitalimages, any other digital content may likewise be managed or handled bythe system provided herein, including video files, audio files, and soforth. While processes or blocks are presented in a given order,alternative implementations may perform routines having steps, or employsystems having blocks, in a different order, and some processes orblocks may be deleted, moved, added, subdivided, combined, and/ormodified to provide alternative or subcombinations. Each of theseprocesses or blocks may be implemented in a variety of different ways.Also, while processes or blocks are at times shown as being performed inseries, these processes or blocks may instead be performed orimplemented in parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various examples described above can be combined to providefurther implementations of the invention.

Any patents and applications and other references noted above, includingany that may be listed in accompanying filing papers, are incorporatedherein by reference. Aspects of the invention can be modified, ifnecessary, to employ the systems, functions, and concepts of the variousreferences described above to provide yet further implementations of theinvention.

Other changes can be made to the invention in light of the aboveDetailed Description. While the above description describes certainexamples of the invention, and describes the best mode contemplated, nomatter how detailed the above appears in text, the invention can bepracticed in many ways. Details of the system may vary considerably inits specific implementation, while still being encompassed by theinvention disclosed herein. As noted above, particular terminology usedwhen describing certain features or aspects of the invention should notbe taken to imply that the terminology is being redefined herein to berestricted to any specific characteristics, features, or aspects of theinvention with which that terminology is associated. In general, theterms used in the following claims should not be construed to limit theinvention to the specific examples disclosed in the specification,unless the above Detailed Description section explicitly defines suchterms. Accordingly, the actual scope of the invention encompasses notonly the disclosed examples, but also all equivalent ways of practicingor implementing the invention under the claims.

1. A method for determining a phase shift of an echoed signal in response to a transmitted signal incident onto an object, the method comprising: receiving a second signal, the second signal being a reflection of a first signal incident on the object, wherein the first signal is modulated by one or more pulses having a defined modulation frequency; determining a first sum of points in time within an overlap region of the first and second signals, wherein the overlap region includes a portion of both respective pulses of the first and second signals; determining a second sum of points in time within the respective one of the pulses of the second signal; and determining a fraction of the first signal that is overlapped by the second signal upon dividing the first sum of points in time by the second sum of points, wherein the phase shift of the second signal is provided upon subtracting the determined fraction of the first signal from a selected value.
 2. The method of claim 1, further comprising modulating the first signal with at least one of triangular pulses, rectangular pulses, square pulses, Gaussian Monocycle, sine pulses, trapezoidal pulses, or any other distinct repeatable signal.
 3. The method of claim 1, further comprising modulating the first signal with the defined modulation frequency determined based at least in part on an expected distance to the object.
 4. The method of claim 1 wherein determining the first sum of points in time includes calculating a convolution of the first and second signals.
 5. The method of claim 4 wherein determining the first sum of points in time includes calculating ∫f_(sent)(t)*f_(reflected)(t)dt, where f_(sent)(t) and f_(reflected)(t) correspond to functions over time of the first and second signals, respectively.
 6. The method of claim 1 wherein determining the second sum of points in time includes calculating an integral in time of the respective one of the pulses of the second signal.
 7. The method of claim 6 wherein determining the second sum of points in time includes calculating ∫f_(reflected)(t)dt, where f_(reflected) corresponds to a function over time of the second signal.
 8. The method of claim 1, further comprising normalizing the first signal to 1 such that the first sum of points in time is equivalent to an integral over time of the second signal within the overlap region.
 9. The method of claim 1 wherein determining the fraction of the first signal that is overlapped by the second signal includes calculating $\frac{\int{{f_{sent}(t)}*{f_{reflected}(t)}{t}}}{\int{{f_{reflected}(t)}{t}}},$ where f_(sent) and f_(reflected) correspond to functions over time of the first and second signals, respectively.
 10. The method of claim 1 wherein subtracting the determined fraction of the first signal from the selected value includes subtracting the determined fraction from
 1. 11. The method of claim 1, further comprising transmitting the first signal onto the object by splitting the first signal into first and second polarizations that respectively incident onto the object.
 12. The method of claim 11 wherein receiving the second signal comprises: receiving a first reflected signal, in response to the first polarization of the first signal incident onto the object; receiving a second reflected signal, in response to the second polarization of the first signal incident on the object; and averaging the received first and second reflected signals.
 13. The method of claim 12 wherein averaging the received first and second reflected signals includes averaging weighted coefficients of the first and second reflected signals.
 14. The method of claim 11 wherein splitting the first signal into the first and second polarizations includes polarizing the first signal with at least one of linear, circular, and elliptical polarization.
 15. The method of claim 11 wherein splitting the first signal into the first and second polarizations includes splitting the first signal into a ⅓ polarization and a ⅔ polarization.
 16. The method of claim 1, further comprising: determining a time shift of the second signal in response to multiplying the phase shift by half a time duration of a respective one of the modulated pulses of the first signal; and calculating a distance to the object upon multiplying the time shift by a speed of light.
 17. A system to determine a phase shift of an echoed signal in response to a transmitted signal incident onto an object, the system comprising: a detecting element configured to receive a reflected signal corresponding to a reflection of the transmitted signal incident on the object, wherein the transmitted signal is modulated by one or more pulses having a defined modulation frequency; and a correlator coupled to receive the transmitted signal and the reflected signal, wherein the correlator is configured to: determine a fraction of the transmitted signal that is overlapped by the reflected signal, in response to dividing a first sum of mutual points in time, between the transmitted signal and the reflected signal, by a second sum of points in time within a respective pulse of the reflected signal, and determine a phase shift of the reflected signal in response to subtracting the determined fraction of the transmitted signal from a selected value.
 18. The system of claim 17 wherein the transmitted signal is a light beam transmitted by a laser diode.
 19. The system of claim 17 wherein the detecting element is at least one of a photocell, photodiode, phototransistor, CCD (Charged Coupled Device), and image sensor.
 20. The system of claim 17 wherein the defined modulation frequency is periodically changed based on a defined sequence.
 21. The system of claim 17 wherein the correlator determines the first sum of mutual points in time in response to calculating a convolution of the transmitted and reflected signals.
 22. The system of claim 21 wherein the first sum of mutual points in time is determined by ∫f_(sent)(t)*f_(reflected)(t)dt, where f_(sent) and f_(reflected) correspond to functions over time of the transmitted and reflected signals, respectively.
 23. The system of claim 22 wherein the transmitted signal received by the correlator is normalized to 1 such that the first sum of mutual points in time is provided by ∫_(t₁)^(t₂)f_(reflected)(t) t, where f_(reflected) corresponds to a function over time of the reflected signal.
 24. The system of claim 17 wherein the correlator determines the second sum of points in time by calculating an integral in time of a respective one of the reflected signal pulses.
 25. The system of claim 24 wherein the second sum of points in time is determined by calculating ∫f_(reflected)(t)dt, where f_(reflected) corresponds to a function over time of the reflected signal.
 26. The system of claim 17 wherein the selected value is
 1. 27. The system of claim 17, further comprising a polarizing splitter configured to split the transmitted signal into first and second polarized signals having different polarizations.
 28. The system of claim 27 wherein the polarization of the first and second polarized signals is non-symmetrical.
 29. The system of claim 27 wherein the first and second polarized signals are p-polarized and s-polarized, respectively.
 30. The system of claim 27 wherein the reflected signal received by the correlator comprises: a first reflected signal, in response to the first polarized signal incident on the object; and a second reflected signal, in response to the second polarized signal incident on the object.
 31. The system of claim 30 wherein the correlator determines an average of the first and second reflected signals upon averaging weighted coefficients of the first and second reflected signals.
 32. The system of claim 17 wherein the correlator is configured to: determine a time shift of the reflected signal in response to multiplying the phase shift by half a time duration of a respective one of the modulating pulses of the transmitted signal; and calculate a distance to the object upon multiplying the time shift by a speed of light.
 33. A method for determining a phase shift of an echoed signal while compensating for noise error in the echoed signal, the method comprising: receiving a reflected signal corresponding to a reflection of a transmitted signal incident on an object, wherein the transmitted signal is modulated by one or more pulses; determining a fraction of an area of the transmitted signal that is common to both the reflected and transmitted signals over a defined interval of time in response to dividing a mutual area of the transmitted and reflected signals over the defined interval of time by a total area of the reflected signal over the defined interval of time; and determining a phase shift of the reflected signal relative the transmitted signal in response to subtracting the determined fraction of the area of the transmitted signal that is common to both the reflected and transmitted signals from a selected value.
 34. The method of claim 33 wherein determining the fraction of the area of the transmitted signal includes convolving the transmitted and reflected signals.
 35. The method of claim 33 wherein the selected value is representative of an ideal reflection.
 36. The method of claim 33, further comprises: determining a time of flight (TOF) of the transmitted signal in response to multiplying the phase shift by a time interval of a respective one of the modulated pulses; and determining a distance to the object in response to multiplying half the time of flight by a speed of the transmitted signal. 